The present invention relates to colored composite microparticles, a dispersion containing the colored composite microparticles, a process for producing the colored composite microparticles, a colorant for color filters, a coloring composition for color filters containing the colorant, a color filter, a colorant for inks for ink-jet printing, and an ink for ink-jet printing. More particularly, the present invention relates to colored composite microparticles having a fine primary particle diameter, and exhibiting a high tinting strength, an excellent dispersibility and an excellent light fastness; a dispersion containing the colored composite microparticles which exhibits an excellent dispersibility; a process for producing the colored composite microparticles; a colorant for color filters, which has a fine primary particle diameter, exhibits a high tinting strength, and is excellent in dispersibility in vehicles, light fastness and heat resistance; a coloring composition for color filters and a color filter which are excellent in light fastness and heat resistance as well as transparency; a colorant for inks for ink-jet printing, which has a fine primary particle diameter and a uniform particle size distribution, exhibits a high tinting strength, and is excellent in dispersibility and light fastness; and an ink for ink-jet printing, which contains the colorant for inks for ink-jet printing, and is excellent in dispersibility, dispersion stability and light fastness.
Organic pigments have been extensively used as colorants in various applications such as paints, resins, printing inks, inks for ink-jet printing, toners and color filters. In these application fields, in general, the pigments have been required to have a high tinting strength. For this reason, it has been required to provide much finer pigments.
The organic pigments are, in general, present in the form of fine primary particles having a particle size of about 20 nm to 100 nm, which are formed from pigments in a molecular state obtained by chemical reaction, etc. However, the organic pigments in the form of fine primary particles tend to be agglomerated together because of a very high surface energy on the particles. For this reason, the organic pigments are usually present in the form of secondary particles having a very large particle size and a high cohesive force. Therefore, it has been required to develop techniques for obtaining very finely divided organic pigments.
At present, as the method for obtaining very finely divided organic pigments, there have been used a wet-pulverization method such as typically a solvent/salt milling method in which pigment particles are mechanically pulverized together with a high-viscous water-soluble organic solvent such as polyethyleneglycol using an abrasive such as a common salt, a dry-pulverization method of pulverizing the pigment particles under a dried condition using a pulverizer such as a ball mill, an attritor and a vibration mill, and a method of forming fine pigment particles by solubilizing pigments to prepare a solution thereof and then precipitating the pigments from the solution under specific conditions.
However, in any of these conventional methods, the finer the particle size of the pigments, the stronger the coagulation force between the pigments particles. In particular, in the wet method using an aqueous system, the coagulation between the particles after drying becomes remarkable, so that it may be extremely difficult to maintain a shape of the primary particles. As a result, the pigment particles are present in the form of secondary agglomerated particles as an aggregate having a very strong coagulation force, so that it may be further difficult to disperse the pigment particles in a solvent.
Also, paints and printed matters using the organic pigments are used outdoors, etc., and therefore, tend to be exposed to direct sunlight, weather, etc. Therefore, the organic pigments have been required to have an excellent light fastness. However, since finer pigment particles tend to exhibit a poorer light fastness, it has been conventionally difficult to produce pigments satisfying both a fine particle size and an excellent light fastness.
On the other hand, color filters have been extensively used in the application fields of monitors for televisions, personal computers, portable telephones, etc., or in the application fields of CCD and CMOS for digital cameras. Among them, the color filters of a pigment-dispersion type are predominately used from the standpoints of a light fastness and a heat resistance. At present, the color filters have been required to exhibit a still higher pixel reproducibility as well as a high contrast. To achieve these requirements, it has also been required that organic pigments used in the color filters are provided in the form of fine particles which can be stably dispersed in a nano level.
The color filters are required to show a good light fastness for preventing the color fading thereof even when irradiated with a backlight, and further required to have a good heat resistance for heat-treating the filters at a temperature of about 250° C. upon hardening of patterns formed thereon or vapor deposition of ITO film thereon. However, the pigments in the form of very fine particles generally tend to be deteriorated in light fastness and heat resistance. For this reason, it has been strongly required to provide a colorant for color filters, which has a particle size in a nano level, can be stably dispersed in vehicles, and is excellent in light fastness and heat resistance.
On the other hand, various OA equipments including personal computers have now rapidly prevailed in both of business and domestic applications. Ink-jet printers as one of recording apparatuses for these equipments have also widely prevailed owing to recent reduction in price and enhancement in quality thereof.
In recent years, the ink-jet printers are capable of realizing a high-level image quality having a high definition and a high gloss, which are almost similar to those of a silver photograph. With the enhancement in image quality, printed matters obtained by the ink-jet printing have been more extensively used in various applications, so that it becomes important that the printed matters have a good keeping property (light fastness) for a long period of time.
Conventionally, as the colorant for inks for ink-jet printing, there have been used dyes from the standpoints of clogging of a head portion of ink-jet printers, dispersion stability and chromaticity of inks, etc. However, the dyes have problems concerning toxicity. In addition, owing to the recent demand for enhanced light fastness of printed matters, it has been attempted to prepare an ink by using pigments as the colorant in place of the dyes.
When using the pigments as a colorant for inks for ink-jet printing, the resultant printed images have a high image density and an excellent light fastness as compared to those obtained by using the dyes as the colorant. However, since the inks for ink-jet printing generally contain water in an amount of 80% by weight of whole constituting components thereof, the pigments, in particular, organic pigments composed of organic compounds, tend to be hardly dispersed therein. In addition, the pigments tend to be insoluble in a solvent such as water unlike the dyes. Therefore, it may be difficult to stably keep the pigment-containing inks for ink-jet printing for a long period of time, and there arises such a problem that the inks tend to cause clogging of a head portion of ink-jet printers. Further, the organic pigments in a molecular state, which are obtained by chemical reactions, etc., and the organic pigments composed of fine primary particles having a particle size of about 20 nm to 100 nm, tend to be agglomerated together because of a very high surface energy on the particles, so that it may be difficult to obtain particles having a uniform particle size distribution, thereby failing to produce a clear image without fogging.
On the other hand, the clogging of the head portion may be prevented by finely reducing a particle size of the colorant. On the contrary, it may be difficult to disperse such a colorant having a fine particle size in an ink composition, and the colorant tends to be deteriorated in light fastness.
As the method of finely reducing the particle size, there has been proposed a method for producing fine particles by adding a small amount of an organic solvent having an effect of promoting a crystal growth to crude quinophthalone pigments or isoindoline pigments having an average particle diameter of more than 100 nm and then pulverizing the resultant mixture by a dry method (Japanese Patent Application Laid-open (KOKAI) No. 2005-36150).
Also, as the colorant in the form of fine particles having an excellent light fastness, there has been proposed an organic and inorganic composite pigment produced by allowing an organic pigment to adhere onto the surface of white inorganic particles through a gluing agent such as an alkoxysilane (Japanese Patent Application Laid-open (KOKAI) No. 2002-356625).
As the colorant in the form of fine particles having an excellent transparency, there have been proposed colored fine particles which are produced by completely dissolving and removing core particles from composite particles obtained by allowing an organic pigment to adhere onto the surface of white inorganic particles as the core particles through a gluing agent such as an alkoxysilane, by using a theoretical amount or more of an acid or an alkali capable of dissolving a whole amount of the white inorganic particles as the core particles (Japanese Patent Application Laid-open (KOKAI) No. 2003-246941).
As the technique for obtaining an organic pigment in the form of fine particles, there has been proposed a method for producing a pigment composition for a blue pixel portion of color filters in which an ε-type copper phthalocyanine pigment as a fine organic pigment and a dioxazine violet pigment having an aspect ratio of 10:1 to 25:1 are subjected together to solvent/salt milling treatment (Japanese Patent Application Laid-open (KOKAI) No. 2006-091649). Also, there has been proposed a method for producing an organic pigment in the form of fine particles by flowing a solution prepared by dissolving the organic pigment in an alkali or acid aqueous medium in the form of a layered flow to change a pH value of the solution in the course of the layered flow (Japanese Patent Application Laid-open (KOKAI) No. 2005-307154).
There have been proposed a coloring composition for color filters, which contains an organic and inorganic composite pigment having an average particle diameter of 1 to 100 nm which is obtained by adhering an organic pigment onto the surface of fine white inorganic particles, and a color filter containing the coloring composition for color filters (Japanese Patent Application Laid-open (KOKAI) No. 2004-307853).
As the ink for ink-jet printing, there has been proposed a water-based recording solution for ink-jet printing, which contains a pigment and colloidal silica for the purpose of obtaining printed images having a high image quality (Japanese Patent Application Laid-open (KOKAI) Nos. 9-227812 (1997) and 2000-53901).
Further, as the colorant in the form of fine particles having an excellent light fastness, there has been proposed a colorant for inks for ink-jet printing, which is composed of composite particles having an average particle diameter of 0.001 to 0.15 μm which are obtained by uniformly adhering an organic pigment onto the surface of extender pigment particles through a gluing agent (Japanese Patent Application Laid-open (KOKAI) Nos. 2003-55591, 2003-268278, 2003-327880 and 2006-111875).